1. Field of the Invention
The present invention relates to the following, by a control authority, of the course of the flight plan of an aircraft provided with a flight management computer FMS (Flight Management System) and linked by a data transmission system to the control authority. It is particularly concerned with the management of air traffic by means of the ATM system (Air Traffic Management system).
2. Description of the Related Art
The air traffic control authorities organize aerial movements within the aerial volumes placed under their control on the basis of 4D flight plans, which are submitted to them in advance by the crews of the aircraft. They verify that the various flight plans submitted are compatible with the safety of the various parties before approving them, then they monitor, during their course, the deviations of the aircraft with respect to the forecast positions and give diversion instructions when these deviations tend to close shaves between aircraft which threaten their safety.
A 4D flight plan defines a 3D trajectory skeleton (latitude longitude, altitude) associated with a travel schedule by means of a chaining of waypoints WP which are located, in the path of the aircraft, at places of change of flight constraints and which are associated individually with various local flight constraints: constraints of altitude, of speed, of capture heading, of escape heading, of ground speed, of vertical speed, of date of transit, etc. The chaining of the waypoints WP defines the lateral projection of the route envisaged. The local flight constraints determine the vertical projection of the route envisaged and the travel schedule. The following of a flight plan by an aircraft consists in homing in on the waypoints WP in the order of their chaining by traveling, between two successive waypoints WP, along a straight segment (or “leg”), in fact a segment of large terrestrial circular arc, while complying with the local constraints associated with the waypoints WP delimiting the ends of the segment.
The crew or the flight management computer FMS of an aircraft determines the 3D trajectory actually followed by the aircraft based on the 3D trajectory skeleton of the flight plan and the travel schedule that are specified in the flight plan, and while taking account of the maneuvering capabilities of the aircraft and a desired degree of comfort. The taking into account of the maneuvering capabilities of the aircraft and of the desired comfort gives rise to the introduction, into the 3D trajectory actually followed by the aircraft of softened transitions between the straight segments of the 3D trajectory skeleton of the flight plan. These softened transitions entail changes of flight constraints at specific waypoints termed pseudo-waypoints PWP which are not mentioned in the flight plan.
The air traffic control authorities use the flight plans which are submitted to them to estimate the instantaneous theoretical positions of the aircraft in their aerial volumes and to evaluate the risks of collision. The evaluation of the risks of collision is done by allocating each aircraft its own protection corridor (a tube-shaped volume placed around the short-term theoretical position of the aircraft and oriented according to the theoretical speed vector of the aircraft) which must not intercept any other protection corridor. The width of the protection corridors takes account of the possibilities of softened transitions between two segments of a flight plan.
For the assessment of the deviations between the actual and theoretical positions of the aircraft with a view to a possible recentring of their protection volumes and of possible avoidance commands for solving newly apparent risks of collision, the air traffic control authorities call upon non cooperative means of tagging of aircrafts such as primary radars but also upon cooperative means making it possible to request information from aircraft regarding their actual instantaneous positions such as transmissions by speech with crews, secondary radars interrogating onboard responders or the ATM system hooked up by data transmission with the flight management computers of the aircraft.
When the ATM system is used, the FMS flight management computer of an aircraft provides on request the instantaneous position and the instantaneous speed vector of the aircraft as well as forecasts of date, of altitude and of speed vector of crossing of a next waypoint WP, thereby enabling the air traffic control authorities to reset the position of an aircraft with respect to its flight plan so as to make it tally with the actual situation.
In view of the softened transitions with which the trajectory actually followed is embellished, an aircraft does not necessarily pass exactly in line with a waypoint mentioned in its flight plan if the overflying of the waypoint is not compulsory. In this case, the instant of crossing of a waypoint is regarded as the instant of nearest approach.